The present invention relates to a resilient bushing for use between a suspension link and a motor vehicle frame or between a suspension link and an axle, and more particularly to a fluid-filled bushing with variable compliance.
When a motor vehicle such as an automobile runs over a bumpy road, noise will be produced and vibration will be transmitted to the passenger compartment if the suspension mechanisms fail to dampen shocks sufficiently which are imposed on the automobile in the longitudinal or fore-and-aft direction thereof. One conventional means for increasing the flexibility of a suspension mechanism in the fore-and-aft direction of the automobile comprises a resilient bushing disposed between a suspension link and an automobile frame or between a suspension link and an axle. The suspension mechanism compliance should be adjusted in view of conditions in which the automobile runs since the attitude or posture of the automobile varies when it is braked, makes a turn, or travels over a rough road. Specifically, it is preferable for the bushing to have a greater degree of rigidity for higher automobile maneuvering stability, increased ability to travel along a straight line at higher speed, or reduced vibration at the start of the automobile. Conversely, the bushing should preferably be of lower rigidity for greater riding comfort and quietness in the passenger compartment.
Japanese Laid-Open Utility Model Publication No. 59(1984)-116649 discloses a typical resilient bushing with adjustable flexibility in the fore-and-aft direction of a motor vehicle. The disclosed resilient bushing comprises inner and outer sleeves disposed concentrically in a frustoconical casing integrally formed with a motor vehicle frame, an intermediate sleeve disposed concentrically between the inner and outer sleeves, and annular resilient bodies interposed between these sleeves. The bushing has first and second fluid chambers defined between the outer and intermediate sleeves in diametrically confronting relation, the first and second chambers being filled with an incompressible fluid such as an antifreeze. The first and second chambers are held in communication with each other through holes defined in the outer sleeve and an annular passage defined between the casing and the outer sleeve. A solenoid-operated spool valve is mounted on an outer peripheral surface of the casing for opening and closing the holes to bring the first and second chamber into and out of communication with each other, thereby adjusting the flexibility or "compliance" of the bushing in the fore-and-aft direction of the motor vehicle. However, the above conventional resilient bushing fails to sufficiently meet various different running conditions of the automobile since the compliance can be adjusted only in two steps by bringing the first and second chambers into and out of mutual communication.